Feral Swine: The California Experience

REGINALD H. BARRETT, Department of Forestry and Resource Management
University of California, Berkeley, CA, 94720

History and Status

Domestic pigs (Sus scrofa) first arrived in California with the Spanish in 1769. Throughout the following century European settlers, including the Russians at Fort Ross, continued to transport domestic swine into the state. Most of these pigs were variously colored mongrels exhibiting short-legged, chuffy, lard pig traits (Barrett 1978). In 1925 Eurasian wild boar stock from North Carolina was introduced by George Gordon Moore to his San Francisquito Ranch near Carmel, Monterey County. Mayer and Brisbin (1991:12-19,58-60,208-209) have compiled an excellent review of the history of wild pigs in California through 1988. The statewide pattern has been one of expanding range, hunter interest and annual kill (Figures 1-4) since the wild pig was declared a game mammal by the California Fish and Game Commission in 1956. I will therefore concentrate on trends over the last 5 years and provide a brief review of wild pig research in the state.

Until 1992, the only systematic, statewide monitoring of wild pigs by the California Department of Fish and Game has been through the annual Game Take Hunter Survey of about 4 percent of licensed hunters. Wild pigs have been monitored in this way since 1956. While long-term trends have clearly been up, most of California has recently been beset by a 6-year drought, which has had a detectable impact on wild pigs (Figures 5, 6). The primary limitation has probably been lack of free water and green feed in the dry Mediterranean summers. Some biologists believe that pumas (Felis concolor) and black bears (Ursus americana), at least locally, have increased predation on wild pigs in recent years. Pumas are no longer game mammals and black bear harvests have been restricted. In any case, it is clear that the wild pig is nearly as important a big game species in California as deer (Figure 7). Wild pig numbers have most recently been estimated at 70-80,000 (Mansfield 1986, Robb 1989).

Increasing concern about effects of wild pigs on native flora and fauna (Willy 1987, Hoffman 1988, Ray 1988, Martin 1990, Nie 1992), particularly by the California Native Plant Society, lead to passage of legislation (Senate Bill 819) in 1991 modifying the Fish and Game’s management program for wild pigs. As of 1992 resident hunters must purchase tags in books of 5 at a cost of $7.90 per book before going hunting (Anonymous 1992). There is no limit on the number of tags purchased, but tag report cards must be returned by the end of the season. Tag fees will be used to develop and implement a statewide, wild pig management plan. The new tag program has not been enthusiastically received by hunters.

Depredations by wild pigs are currently handled by providing a landowner with a permit to remove the depredating pigs within a specified period of time after inspection of the damage by a warden. Carcasses must be turned over the the warden. Alternatively, the warden may authorize a currently licensed California hunter to take and possess 2 pigs per day on designated lands. In this case the hunter retains the carcasses. It is likely that with a few years of good rainfall, wild pig numbers will once again expand, resulting in more conflict and additional legislation regarding wild pig management in California.

Research

Biologists with the California Department of Fish and Game were the first to initiate modern scientific research on the wild pig in California. The first project concentrated on the Hunter-Ligget Military Reservation in Monterey County with a goal of determining appropriate hunting regulations to sustain public hunting (Pine and Gerdes 1973). This intensive management program in cooperation with the U.S. Army is ongoing (Mansfield 1978).

The second project was supported by the Dye Creek Preserve in eastern Tehama County. The goal was to find an economic solution to an apparent conflict between wild pigs and cattle production on private rangeland (Barrett 1970, 1971, 1978, 1982, 1984). A fee hunting enterprise was established that more than covered the cost of wild pig control (Patten 1974); the program remains in operation despite change in ownership of the property.

The third project was initiated by the California Department of Fish and Game on private land in San Luis Obispo County to determine proper hunting regulations (Edon 1974). This work highlighted the fact that it is difficult for a typical California rancher to manage pigs without cooperation among neighboring properties.

The fourth project was sponsored by the California Agricultural Experiment Station and the Department of Fish and Game to test methods for carrying out a statewide survey of wild pigs (Barrett and Pine 1980). This work never proceeded beyond a pilot project in San Benito County. Constructing a detailed map of the distribution of wild pigs throughout California is still a top research priority.

Next, a basic ecological study of wild pigs in Grant County Park, Santa Clara County was sponsored by the county and San Jose State University (Schauss 1980, 1990). The county concluded it could live with the pigs.

The Department of Fish and Game sponsored a project to determine proper hunting regulations for wild pigs on the Cottonwood Wildlife Management Area, Santa Clara County (Klein 1981). Here again it became clear that any intensive management would require cooperation among neighboring landowners. Cooperation was not forthcoming in this instance.

The Nature Conservency sponsored a study of wild pigs at their North Coast Preserve, Mendocino County in hopes of determining ways to minimize damage by pigs to native flora and fauna (Grover 1983). Food habits and movement information was obtained, but there was no resolution of the damage issue. The University of California now manages the property and a study is in progress on the response of native grasses to rooting.

Next, the Catalina Conservency and Oregon State University sponsored the first basic ecological study of wild pigs on one of the Channel Islands, Los Angeles County (Baber 1985, Baber and Coblentz 1986, 1987). Management on Santa Catalina has recently shifted from long-term control via fee hunting to an intensive removal effort.

The Nature Conservency then sponsored a wild pig study on Santa Cruz, another of the Channel Islands, Santa Barbara County (Van Vuren 1984). This work was done in conjunction with the successful effort to remove feral sheep from the island. A small study of foraging behavior was also done at this time (Krosniunas 1985).

The California Department of Fish and Game has sponsored serological and other studies of disease status among wild pigs throughout the state (Smith and Latham 1978, Clark et al. 1983, Powers 1984, Nettles et al. 1989, Drew et al. 1992). Implication of wild pigs as vectors of bovine tuberculosis in San Luis Obispo County in 1965 has been the only serious disease problem to date.

The California Department of Parks and Recreation sponsored a major project to demonstratate the feasibility of removing all wild pigs from Annadel State Park, Sonoma County. This was accomplished over a 3-year period (Barrett et al. 1988).

A similar pilot project to estimate the cost of removing all pigs form Santa Cruz Island was sponsored by The Nature Conservency. All pigs were successfully removed from a 5,000-acre pasture (Sterner 1990, Sterner and Barrett 1991). Unfortunately funds were not forthcoming to complete the removal island wide. The National Park Service has proceeded to remove all wild pigs from nearby Santa Rosa Island.

A number of additional projects have gone unpublished. However, it is clear that the majority of funding for research has gone towards resolving real or perceived conflicts between wild pigs and domestic livestock or native flora and fauna. Little effort has gone towards documenting such conflicts (de Nevers and Goatcher 1990).

Conclusions

Wild pigs will continue to expand their range and numbers throughout the oak woodland and chaparral regions of California unless there are concerted efforts to reverse this trend. Drought and mast failures will only temporarily reverse the long-term trend. Along with this increase in wild pigs will come an escalation of controversy between sport hunting and nature preservation interests. The Department of Fish and Game now has the legislative mandate and the financial means to produce a management plan for wild pigs in California that hopefully will accommodate the desires of both groups. Such a plan must acknowledge a policy of: 1) removing wild pigs from parks and nature preserves to the extent feasible, 2) discouraging the illegal introduction of wild pigs into new habitats, 3) promoting the use of sport hunting to control pig numbers where they cannot be eliminated, and 4) encouraging monitoring and basic ecological research on wild pigs, including their effects on native ecosystems.

Literature Cited

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